A model system for studying chemical carcinogenesis in colon has been developed. Human colon can generally be maintained 7-24 days and rat colon at least 63 days as explant cultures. Cultured human and rat colon have the ability to enzymatically convert various classes of chemical carcinogens, such as polycyclic aromatic hydrocarbons, N-nitrosamines, mycotoxins and hydrazines, into metabolites which react with cellular macromolecules, such as DNA and protein. A 100-fold interindividual variation in the binding of benzo(a)pyrene (BP) and a 60-fold variation in the binding of 1,2-dimethylhydrazine (DMH) to DNA was found. A positive correlation in the binding level of BP and DMH to DNA was observed. The carcinogen-DNA adducts for aflatoxin B1, BP, N-nitrosodimethylamine and DMH have been identified, and were qualitatively similar in both rat and human colon.